Demonstration of Thin Film Bulk Acoustic Resonator Based on AlN/AlScN Composite Film with a Feasible

• Published in: Micromachines (Basel) Vol. 13; no. 12; p. 2044
• Main Authors: Laixia Nian, Yang Zou, Chao Gao, Yu Zhou, Yuchen Fan, Jian Wang, Wenjuan Liu, Yan Liu, Jeffrey Bowoon Soon, Yao Cai, Chengliang Sun
• Format: Journal Article
• Language: English
• Published: MDPI AG 01-11-2022
• Subjects: aluminum scandium nitride; composite film; effective electromechanical coupling coefficient; film bulk acoustic resonator
• ISSN: 2072-666X
• DOI: 10.3390/mi13122044

Film bulk acoustic resonators (FBARs) with a desired effective electromechanical coupling coefficient ( Keff2 ) are essential for designing filter devices. Using AlN/AlScN composite film with the adjustable thickness ratio can be a feasible approach to obtain the required Keff2 . In this work, we research the resonant characteristics of FBARs based on AlN/AlScN composite films with different thickness ratios by finite element method and fabricate FBAR devices in a micro-electromechanical systems process. Benefiting from the large piezoelectric constants, with a 1 μm-thick Al0.8Sc0.2N film, Keff2 can be twice compared with that of FBAR based on pure AlN films. For the composite films with different thickness ratios, Keff2 can be adjusted in a relatively wide range. In this case, a filter with the specific N77 sub-band is demonstrated using AlN/Al0.8Sc0.2N composite film, which verifies the enormous potential for AlN/AlScN composite film in design filters.